Few industrial applications demand as stringently clean a working environment as paint facilities. Even the most advanced robotic paint systems are subject to contamination, and even the smallest contaminant can ruin an otherwise perfect finish. Thus, the painting equipment must be kept clean and must be isolated from the painted surfaces so that contaminates from the equipment may not migrate from the equipment to the painted surface.
Typically, in high volume, high value manufacturing facilities, robotic painters are employed along with electrostatic spray guns. The robotic painters allow for automating the painting process. Yet, the robots tend to generate particles as the arms of the robot move. Moreover, lubricants and other working fluids (e.g. compressed air or hydraulic fluid) may escape in minute amounts. Even these minute amounts of contaminants may disadvantageously impact the quality of the finished surface.
Additionally, the electrostatic spray guns employed also contribute to the contamination level. Material sprayed from the gun may entrain contaminates from the robot and carry them to the painted surface. Furthermore, the differential charge applied between the gun and the painted surface, which attracts the paint to the surface, also attracts charged particles from the gun and the robot. Thus, painting robots, as well as other types of painting equipment, act as a source of disadvantageous contamination.
One solution to the painting equipment itself being a source of contaminates, and to keeping the equipment clean, has been to apply a cover over the equipment to prevent migration of contaminates to the painted surface. These covers typically include an opening for the nozzle to extend from the cover yet otherwise surround the robot. Thus, the cover traps the vast majority of contamination from the robot. These covers have been well received by the industries in which consumers demand high quality finished surfaces. In particular, TD Industrial Coverings of Sterling Heights, Mich. has supplied the automotive industry numerous high quality industrial covers.
As previously mentioned electrostatic spray guns use electrostatic attraction to assist in painting the surface. Such an approach improves the transfer efficiency of the spray gun by ensuring that more of the paint reaches and sticks to the surface to be painted. Moreover, by improving the efficiency of the electrostatic spraying devices, fewer paint fumes escape the manufacturing facility than with conventional (non electrostatic) spray guns.
Despite the use of electrostatic spray guns, paint particles may still escape deposition on the object for a variety of reasons. For instance, the object to be painted may include geometry which makes the object difficult to paint, thereby requiring more paint to be applied than would otherwise be the case. Examples of difficult geometry include narrow grooves and other recesses with sharp aspect ratios. Difficulties in atomizing the paint may cause larger than optimal drops to form which gravity causes to fall from the spray. Variations in the compressed air supply pressure may deviate from the optimal range. Likewise, electromagnetic fields from nearby devices may alter the path of the paint particles. Or drafts in the painting area, or booth, may cause the spray pattern to drift from the object.
To use these electrostatic spray guns the object to be painted is initially charged with one polarity of electrical charge. The paint is charged with the opposite polarity. As the paint discharges from the gun, the charge on the object attracts the oppositely charged paint droplets. Accordingly, the paint preferentially travels toward the object whereas conventional spray guns produce a cloud of paint particles which are more likely to partially disperse on their way to the object.
Even electrostatic spray guns however suffer from disadvantages. For instance, some of the paint particles will drift from the spray pattern even if charged. Thus, a need exists to improve the efficiency of electrostatic spray guns still further. Additionally, as the charged paint particles encounter the oppositely charged object the energy used to charge the paint particles and the object is used. The flow of charge (on the paint particles) therefore represents a power consuming electrical current that must be continuously re-supplied. Accordingly, an electrostatic spray gun requires power from an electric utility or cogeneration unit. Thus, a need exists to lower the power requirement of existing electrostatic spray guns.